Rheostat



F. A. ROJAS.

RHEOSTAT.

APPLICATION FILED FEB. 20. 1919. 1,366,945.

Patented Feb. 1, 1921.

4 SHEETS-SHEET I- F. A. ROJAS.

- RHEOSTAT.

APPLICATION FILED FEB. 20.1919. 1,366,945. Patented Feb. 1,1921.

4 SHEETSSHEET 2.

F. A. RUJAS.

HHEOSTAT.

AI'ILICMHUN FILED H58. 20. I919- l,366,945. Patented Feb. 1, 1921.

4 SHEETS-SHEET 3.

F. A. ROJAS.

RHEOSTAT.

APPLICATION FILED FEB. 20, 1919. 1,366,945. Patented Feb. 1,1921.

4 SHEETS-SHEET 4- ill (Manama To all whom it may cancer a:

Be it known that i, Fnomonn A. Bowls, a citizen of the Republic of Santo Domingo, and resident of the borough of Manhattan and the city and State of New York, have invented a new and useful improvement in .Rhecstats, of which the "following is a speci fication.

My invention relates to improvements in electric controlling devices in WT. on the electric conductance of the specially arranged conductive and non-conductive stances is made to vary by compressing orexpanding them between two bodies. This combination of conductive and non-cone. tive substances constitutes what will be called my and will resistance material, totally or partially take the place of the resistance coil of the ordinary rheostat.

The objects of my invention first to provide a rheostat so constructed that its resistance can be made to vary consecutively from'a very high degree of resistance down to a small traction of an ohm; second at ford facilities for increasing; the ampere carrying capacity of the rheostat; third, to afford means by which the resistance terial can be so arranged as to have the value of its specific resistance and of its length and cross section suit the; electrical dimensions of the circuit which the rheostat is to con "trol; fourth to provide means for auto matically varying the density of the resistance material, as a whole, in order to main tain the resistance of the rheosta't at a predetermined degree; fifth to provide means for mechanically controlling the operation of the said automatic means for varying the density of the resistance material; sixth, to provide means for maintaining an even distribution of the resistance material; and

seventh, to provide [certain improvements in the form, construction, arrangement and composition or": the several parts, whereby the above named and other objects may be effectively attained.

Practical embodiments of my invention are represented in the accompanying drawinns, in which-- Fig'ure 1 represents a plan view, partly broken away, of the preferred form. Fig. 2 represents a section talren plane of the line illl: of 1, loot the direction of the arrows. v

Fig. 3 represents a. detail section s e means for securing certain parts to 3:1: en se us n 1 J L- 'i L .e nt a Cietdll section snow- 121%; means for securing other parts together. Jig. t represents a tace view, partly sroken away, or a modified form of my invention.

Fig. 5 represents a section taken in the plane of in the direction of the arrows.

Fig. 6 represents a detail rear elevation the device shown in Fig. l, tne course the electric current being indicated diaranmiatically.

1 Fig. 7 represents a detail section, partly oroken away plane of the line Vii-Ill of Fig. 9.

Fig. 8 represents a section taken substantially in the plane of the line VllL-Vlli 9, looking in the direction of the arrows.

Fin". 9 represents a section taken substantially in the plane of the line l) l o i looking in the direction of the arig. 1O rep-resents a view similar to Fig.

5, certain parts being shown in side eleva- 'tion, including a modified form of arrangement of the resistance materialI Fi 11 represents a central section through a modified form of terminal plate and thermostatic device.

Fi 12 represents a detail plan view, partly broken away, showing another modiiied :torm of terminal plates, and

Fig. 13 represents a section taken substantially in the plane of the line Kill- XHI of Fig. 12, looking in the direction of We O o his i the arrows.

Referring to the form shown in Figs. 1 to 3* inclusive, the device comprises a casing 1 which isiitted to rest upon a base 2, that may be-fconveniently composed of slate or other similar material; and the said casing base are secured to some appropriate support, such as a wall. 3, by a means of stud bolts t which pass completely through the device and are threaded at their outer ends for the reception o-=nuts 5 th tbear npon the top of the casing 1.

ll 1 are a pairot termiplates, the outer one of which is deby 6 a d is substantially flat. This plate may L c '"enosed oi": some metal such and it is yieldingly supported withl hy means of a spring Y the e fixed to the upper part of lay bolts 8, 9. The plate the line V-V of Fig. 4-, looking taken substantially in the,

6 is fastened to the spring 7 by a screw 10 which passes through the said plate and spring and is threaded into one member 11 of a loose coupling. The said member 11 is bifurcated and carries in its bifurcation a pin 12 that pierces the adjacent end of the other member 13 of the said coupling. This coupling may be composed of suitable metal, such as iron, and the member 13 is fastened to a head 14 by means of insulated screws 15, while the said member is insulated from the said head by a strip of suitable insulating material 16.

The head 14 has a centrally disposed recess 17 in its outer face which is fitted to receive the inner end of a hand screw 18. Th3 inner end of the said screw carries a cr ss bar 19, and a perforated plate 20 is fixed to the head 14 by screws 21. The erforation of the plate 20 is large enoug to surround the shank of the hand screw 18 but is less in diameter than the length of the cross bar 19so that the said screw and head 14 are loosely coupled together. The screw 18 is threaded into the top of the casing 1. i

F rom' the construtcion just described it will be seen that, when the hand screw is screwed inwardly it will force the terminal plate 6 in a similar direction against the yielding resistance of the spring 7. Thus the combined action of the hand screw 18 and spring 7 serves to determine the position of the terminal plate 6. The loose coupling connections between the screw 18 and plate 6, provide, in effect, a universal joint, so that the plate 6 may, within certain limits, accommodate itself to the material with which it contacts (as will be hereinafter described) in order to provide an equal pressure upon all parts thereof. A tail nut 18* serves to lock the hand screw 18 in any desired adjustment.

It will be observed by reference to Fig. 2 that the spring 7 is insulated from the bolt 9 as indicated at 22, while it is in electrical contact with the bolt 8. Thus the bolt 8 constitutes one of the terminals or binding posts of the device.

The other terminal plate is cup-shaped in form and is composed of iron or similar metal and divided into two parts denoted by 23 and 24. The part 23 is shaped like a flanged collar and it is secured to the upper part of the casing 1 .bythe bolts 8 and 9 and by two other bolts 25. The part 24 is dishlike in form and has a peripheral flange which is also engaged by the bolts 8, 9 and 25 so as to hold the said part 24 in position adjacent its companion part 23.

Within the terminal plate 23, 24 1 locate a thermostatic element which consists of a sheet of metal such as brass, zinc or other metal having a greater co-efiicient of expansion than iron.

This sheet is indicated by 26 and is located between the parts 23 and 24 of the inner terminal plate and has its outer edge fixed to the flange of the latter, by means of screws 27. It will be noticed that said screws have taper heads which are adapted to be countersunk in the flange of the part 24 so as to grip a portion of the sheet 26 therebetween, as indicated at 28 Fig. 3*. It will also be observed that the flange of the part 24 has a shoulder 29 against the inner side of which the sheet 26 abuts; the purpose of this shoulder being to assist in preventing the sheet 26 from expanding laterally under the influence of heat when the device is in use.

The thermostatic sheet 26 is centrally secured by means of a screw 30 to a metallic disk 31 which may be composed of iron or other similar metal. The disk 31 has a circular rib 32 formed thereon which abuts the sheet 26, whereby the said rib, together with the screw 30, causes-the sheet 26 to have a double bend in cross section.

Mechanism for mechanically controlling the action of the thermostatic elements 26 is provided, and consists in aram 33 that has a broad flat head slightly less in diameter than the inside diameter of the circular rib 32 of the disk 31. This ram is fitted to slide in a square socket 34 fashioned on the inside of the part 24, and it has a threaded engagement with a screw 35 that passes freely through the bottom of the part 24. A cross bar 36 pierces the screw 35 within the part 24 to prevent axial outward movement of the said screw. As a result of this construction it will be seen that when the screw 35 is turned in an anti-clockwise direction the ram 33 will be urged forwardly so as to bear upon the thermostatic sheet 26 and force it inwardly or prevent it from bowing further outwardl A look nut 37 serves to fix the screw 35 n any desired adjustment.

The part 23 of the inner terminal plate has a lining of asbestos 38, and the said part is filled with resistance material 39 which contacts with the terminal plate 6 and the disk 31. This resistance material 39 may be composed of conductive and non-conductive substances, mixtures of powders, granular elements, or filaments in a variety of forms and in accordance with the object in view. For instance, a non-conductive owder mixed with a conductive powder; a ody of non-conductive filaments or fabric impregnated by a conductive powder; two conductive powders, one having a positive and the other a negative tem )erature coefficient mixed with a non-con uctive powder; a body of non-conductive filaments or fabric impregnated by a mixture of conductive powders onehaving a positive and the other a negative temperature co-efiicient.

Examples of these mixtures are as follows. First, asbestos powder and powdered graphite; second, granules of graphite or metal filings mixed with asbestos powder, powdered mica, glass or the powder of any refractory non-conductive substance; third, powdered graphite and asbestos filaments or cotton fabric; and fourth, graphite in powdered or granular form, powdered German silver or manganin alloy with asbestos powder or filaments. I prefer a material composed of asbestos fiber and graphite.

I amv aware that prior to my invention rheostats have been made based upon the principle of imperfect contact between solid conductors, as for instance piles of graphite blocks intervening between two compressing bodies. In such devices, a sudden rush of current of an appreciable strength takes place at the critical point where least contact occurs. This differs altogether from one of the main objects of my invention, which is to construct a rheostat whose resistance can. be made to vary from the highest possible degree down to the smallest fraction of an ohm and which will afford any desired degree of resistance between these two points. Such a variation is not possible with carbon piles or any other such arrangement of solids, but is accomplished by the composition of conductive and non-conductive substances of the nature and arranged substan tially as I have described.

The inner surface of the plate 6 and disk '31 are coated with some adhesive or sticky material such, for instance, as a heavy oil mixed with powdered graphite. I do not intend however, to limit my inventionto the use of this particular sticky substance. This substance causes the adjacent resistance material 39 to adhere to the surface of the plate 6 and disk 31 so that, when the said plate and disk are drawn apart, the resistance material will be positively drawn apart so as to lessen its density as a whole, thereby increasing the resistivity of the said material. On the other hand, when the distance between the plate 6 and disk 31 is lessened, the resistance material will be compressed and its resistivity decreased. The fact that the part 23 is flared outwardly toward the plate 6 enables the material 39 to be drawn apart freely. Thus it will be seen that the device can be set or adjusted to furnish a desired. degree of resistance by screwing the 18 inwardly or outwardly so as the reslstance material 39 or this adjustment 18 very hand screw to compress separate. it. While satisfactory, generated by the electric current passing through the device warms-up the resistance material 39 and thereby increases its conductivity so as to modify the actual resistance furnished by the device. In my construction this action is automatically compensated by the action of the thermostatic sheet 26 which, which expands a base 63 (see it often happens that the heat 7 more rapidly than the iron or other metal of which the part 24 is composed, and being unable to spread out laterally under the influence of the heat, expands or bows outwardly toward the bottom of the part 24. This expansion carries the disk 31 along with the sheet 26 and thus increases the distance between the disk 31 and the terminal plate 6 as well as positively drawing the resistance material 39 apart and thereby decreasing its resistance, so as to compensate for the increased conductivity of the resistance material due to its elevated temperature. By this action the resistance of the device as a whole is maintained constant. The disk 31, being of rigid construction, maintains its inner face in parallelism with the adjacent surface of the plate 6, no matter what shape is assumed by the sheet 26; hence there is no opportunity for a short cut to be offered the current by reason of the plates being nearer together at one point than at another. I have found this disk to be advantageous in many cases, but not essential.

In case the sheet 26 should, through continued use, become weakened so as not to be absolutely accurate in its thermostatic action and acquire a tendency to expand too rapidly, the ram 33 may be operated to bear against it, and limit its expansion toward the bottom of the part 24:. It will be seen that the head of the said ram fits within the rib 32 of the disk 31 so that, when the ram is brought into contactwith the sheet 26 the effect is to tighten the latter and make it conform more nearly to the contour of the said disk. Thus any excessive slackening or binding of the sheet 26 maybe easily pre vented or compensated. It will be observed that the terminal plate 23, 24 is in electrical contact with the bolt 9 while it is insulated from the bolt 8 as indicated at 41, 42. Therefore the bolt 6 constitutes the other terminal or binding post for the instrument.

The casing 1 is provided with hand holes l3 in its bottom which provide access to the screw 35 and also serve to cool the device.

Referring to the modified form shown in Figs. 4, 5, 6, 7, 8 and 9, the device comprises Fig. 9) which may be composed of some suitable non-conductive material and is fitted to be secured to stud bolts 6%, protruding from some suitable support such as a wall 65, by means of nuts 66. These nuts also serve to secure the frame work or casing 67 to the base 63.

T he outer plate or terminal is denoted by 66 and is suspended in a manner similar to the plate 6 in the form shown in Figs. 1 and 2 inclusive, by

means of a spring 69 which of this arrangement is to provide means for causing the resistance material, denoted by M, to cling to the plate 68, so that the resistance material will be positively drawn upwardly with the plate 68 when the latter is permitted to rise under the influence of the spring 69. I may also coat the under surface of the plate 68 with an adhesive to aid "this function. as described in connection with the rm shown in Figs. and 2.

ate 88 is secured to the spring late and s 'ng are secured a ece 75 (see Fi 's screw insulate tie pone-rations eing arfered relation inthe resistance by requiring the curto follow an indirect path. The whole 1 side of the plate 82 is covered with an insulation 8 1-.

the bottom of the plate 82 I locate a thermostatic element which is composed of substantially fiat member 85 and a relatively bowed member 86, the two members being firmly secured together ripheries by bending the metal, or in any other approved manner. The member 85 may be composed of Zinc or brass, the member 86 of iron. The result of this arrangement is that, when the instrument is subjected to the heat of an electric current, the member 85 will expand more rapidly than the member 86, and will draw the latter downwardly toward the member 85, thus increasing the space between the member 86 and the plate 68. This movement lessens the compression of the resistance material 74; and by coating the member 86 with an adhesive, as already mentioned,

'70, Cl and by that is fixed at their pethe action will be to positivel draw the resistance material apart. T 1e thermostatic element 85, 86 is brought into contact with the plate 82 by means of a screw 87 which pierces the insulation 84.

The plate 85) is supported by the bolts two other bolts 88, 89. Three of these bolts, to wit, 70, 71 and 88 are insulated from the plate 82, as clearly shown in ig. 8. The spring 69 which supand is in electric contact with the the bolt "3'0 but is i the bolt 71. rve bind-' :l shuna coils s '.-h are secured to 'ed ie base 83 and to a oss bar 92 that is secu to the back of the said base and is in electrical contact with the binding post i'l, as clearly shown at 93 Fig. 6. A. series of knife switches 94, one for each shunt coil, are mounted on. the base 68 and bolted to a Second cross bar 95 to the back of the base and is in electrical contact with the binding post 89, as shown at 96 Fig. 6. The bolts 91 are provided with bifurcated ends 97, fitted to receive the switches 94L in the customary manner. By this construction, when it is desired to increase the resistance of the instrument as a whole, it is simply necessary to throw in one or more of the knife switches 91, so as to bring one or more of the shunt coils into the circuit. The course of Checurrent is diagrammatically indicated by the lines and arrows in Fig. 6. These shunt coils may vary as to their resistance, so that the instrument may be brought into the desired condition of resistance by selecting any one of the switches 94 and throwing it into contact.

The form shown in Fig. is the same deas IOU

ascents as that just described except that the perio. rated insulating disks 83 are omitted, thereby decreasing the resistance.

In Fig. 11 I have shown another modified form of thermostatic element, in which there is employed a single disk or diaphragm 98. This diaphragm may be composed of brass or zinc, and is secured to a terminal plate 99, similar to the plate 82, by the bolts 70, 89. This diaphragm is in electrical contact with the binding post 89, but is insulated from the bolt 70 and the plate 99; lln this construction the diaphragm 98 will expand more rapidly, under the influence of heat, than will the plate 99, and hence will be bowed downwardly toward the dotted line position, so as to decrease the compression of and draw apart the resistance material 74. The diaphragm may be provided with the adhesive as already described. l have found a thermostatic element of this construction desirable in dealing with currents of high voltage.

Referring to the form shown in Figs. 12 and 13 it is the same as the form shown in Figs. 4 to 9 inclusive, except as to the terminalplates 68 and 82. this form lower terminal plate is denoted by 100 and is provided with a series, in the present instance five, of cells 101 to receive the resistance material. Each of these cells 101, has a thermostatic element similar to that shown in Fi s. l to 9, and l have shown the insulating disks 83 as being omitted, though they may be used if desired. The upper terminal plate is indicated b 1102, and a set of knobs 103 which are adapted to enter the cells 101. The operation oi this "form is the same as that already described, but, by the provision of a plurality of cells holding the resistance material, prevent the latter from collecting at one part of the instrument when is seci 5 vertical position. Thus an even tion of the resistance material is maintained, which is highly desirable feature.

will be understood that various changes may be resorted tom the form, censt and arrangement oi the several parts i out departing "from the spirit and e I my invention, and hence T i do to be limited to the details herein shown described except as they may be includes the claims.

Vlfhat I claim is 1; In a rheostat, a pair a compressible resistance material bctwec the terminals, and thermostatic means i: tematically decreasing the compressi n of the said material as its tempei'atu creases, whereby the resistance at the r. s remains constant, i'inostp means including two members cc posed material having difierent coefficients of expansion, said members being of dilierent between the terminals for automatically decreasing the compression of the said 1na terial as its temperature increases, whereby the resistance of the rheostat remains constant, said thermostatic means including two members composed of material having ditfercnt co-efilcients of expansion, said members being of diilerent shape and being socured together, so that the difference in expansion of the two will alter the shape of one.

8. in a rheostat, a pair of terminals, one of said terminals having a plurality of cells, a compressible resistance material located in said cells between the terminals, and means for varying the, compression of the said material.

1-. ln a rheos'tat, a pair of terminals, one of said terminals having a plurality of cells, a compressible resistance material located in said cells between the terminals, and means for automatically decreasing the compression oi' the said material as its temperature increases, whereby the resistance of the rheostat remains constant.

5. a rheostat, a pair of terminals, a cmpressible resistance material between the .lillttlS, means for automatically decreas the compression oi the said material as urality of shunt coils, and means for ringing one or more of said coils into the circu't to alter the resistance 0' the rheostat. n. rheostat, a pair of terminals, a ssible resistance material between the als, me ns for automatically decreasie corn essicn oi the said material .pers vure increases, whereby the sistance h traiity shunt coils of different resist e, and means for bringing ne or mo e or ressible nals, means for automaticthe compression of the sai temperature increases, wheieby cc of the c for "teens "for automatic... creasing the compression of terial as its te the resistance of stant, means for iperature increases, whereby the rheostat remains congoverning said automatic 3 Cit means, and means for adjusting one of the terminals to vary the compression of the material.

9. In a rheostat, a pair of terminals, a compressible resistance material between the terminals, thermostatic means for automatically decreasing the compression of the said material as its temperature increases, whereby the resistance of the rheostat remains constant, and means for governing said thermostatic means.

10. In a rheos-tat, a pair of terminals, a compressible resistance material between the terminals means for automatically de-' creasing the compression of the said material as its temperature increases, whereby the resistance of the rheostat remains constant, and manually controlled means for governing said automatic means.

11. In a rheostat, a pair of terminals. a compressible resistance material between the terminals, means for automatically decreasing the compression of the said material as its temperature increases, whereby the resistance of the rheostat remains constant. manually controlled means for governing said automatic means, and means for adjusting one of the terminals to vary the compression of the material.

12. In a rheostat, a pair of terminals, a compressible resistance material between the terminals, thermostatic means for automatically decreasing the compression of the said material as its temperature increases,

terminals being whereby the resistance of the rheostat remains constant, and manually controlled means for governing said thermostatic means.

13. In a rheostat, a pair of terminals, a compressible resistance material between the terminals, and thermostatic means forautomatically decreasing the compression of the said material as its temperature increases, whereby the resistance of the rheostat remains constant, said thermostatic means being connected with one of the terminals and including a member adapted to alter its shape under the influence of heat, and a device for maintaining the adjacent faces of the terminals in substantial parallelism irrespective of the shape assumed by the said member.v

14. In a rheostat, a pair of terminals, a compressible resistance material between the terminals, means for causing the material to adhere to the terminals, one of said movable outwardly from the other for positively drawing the material apart, and means surrounding the material, said last named means being flared in the direction of outward movement of the movable terminals so as not to hamper the drawing apart of the material.

In testimony, that I claim the foregoing as my invention, I have signed my name this third day of February 1919.

FLORICEL A. ROJAS. 

